my favourite seiyuu is Aya Hirano, because she has such a cute voice, but she can easily change it as well. and i love her songs too...she is the seiyuu of Haruhi (Suzumiya Haruhi no Yuutsu), and Misa (Death Note) to name a few...there are a lot more, but i can't remember them at the moment...

my second favourite is Rie Kugimiya, and she has a really cute voice as well. she is the seiyuu of Shana (Shakugan no Shana), Louise (Zero no Tsukaima), and Rizel (Rizelmine).